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    SubjectRe: [PATCH bpf-next v1 1/9] bpf: Add mkdir, rmdir, unlink syscalls for prog_bpf_syscall
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    On 2/25/22 3:43 PM, Hao Luo wrote:
    > This patch allows bpf_syscall prog to perform some basic filesystem
    > operations: create, remove directories and unlink files. Three bpf
    > helpers are added for this purpose. When combined with the following
    > patches that allow pinning and getting bpf objects from bpf prog,
    > this feature can be used to create directory hierarchy in bpffs that
    > help manage bpf objects purely using bpf progs.
    >
    > The added helpers subject to the same permission checks as their syscall
    > version. For example, one can not write to a read-only file system;
    > The identity of the current process is checked to see whether it has
    > sufficient permission to perform the operations.
    >
    > Only directories and files in bpffs can be created or removed by these
    > helpers. But it won't be too hard to allow these helpers to operate
    > on files in other filesystems, if we want.
    >
    > Signed-off-by: Hao Luo <haoluo@google.com>
    > ---
    > include/linux/bpf.h | 1 +
    > include/uapi/linux/bpf.h | 26 +++++
    > kernel/bpf/inode.c | 9 +-
    > kernel/bpf/syscall.c | 177 +++++++++++++++++++++++++++++++++
    > tools/include/uapi/linux/bpf.h | 26 +++++
    > 5 files changed, 236 insertions(+), 3 deletions(-)
    >
    > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
    > index f19abc59b6cd..fce5e26179f5 100644
    > --- a/include/linux/bpf.h
    > +++ b/include/linux/bpf.h
    > @@ -1584,6 +1584,7 @@ int bpf_link_new_fd(struct bpf_link *link);
    > struct file *bpf_link_new_file(struct bpf_link *link, int *reserved_fd);
    > struct bpf_link *bpf_link_get_from_fd(u32 ufd);
    >
    > +bool bpf_path_is_bpf_dir(const struct path *path);
    > int bpf_obj_pin_user(u32 ufd, const char __user *pathname);
    > int bpf_obj_get_user(const char __user *pathname, int flags);
    >
    > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
    > index afe3d0d7f5f2..a5dbc794403d 100644
    > --- a/include/uapi/linux/bpf.h
    > +++ b/include/uapi/linux/bpf.h
    > @@ -5086,6 +5086,29 @@ union bpf_attr {
    > * Return
    > * 0 on success, or a negative error in case of failure. On error
    > * *dst* buffer is zeroed out.
    > + *
    > + * long bpf_mkdir(const char *pathname, int pathname_sz, u32 mode)

    Can we make pathname_sz to be u32 instead of int? pathname_sz should
    never be negative any way.

    Also, I think it is a good idea to add 'u64 flags' parameter for all
    three helpers, so we have room in the future to tune for new use cases.

    > + * Description
    > + * Attempts to create a directory name *pathname*. The argument
    > + * *pathname_sz* specifies the length of the string *pathname*.
    > + * The argument *mode* specifies the mode for the new directory. It
    > + * is modified by the process's umask. It has the same semantic as
    > + * the syscall mkdir(2).
    > + * Return
    > + * 0 on success, or a negative error in case of failure.
    > + *
    > + * long bpf_rmdir(const char *pathname, int pathname_sz)
    > + * Description
    > + * Deletes a directory, which must be empty.
    > + * Return
    > + * 0 on sucess, or a negative error in case of failure.
    > + *
    > + * long bpf_unlink(const char *pathname, int pathname_sz)
    > + * Description
    > + * Deletes a name and possibly the file it refers to. It has the
    > + * same semantic as the syscall unlink(2).
    > + * Return
    > + * 0 on success, or a negative error in case of failure.
    > */
    > #define __BPF_FUNC_MAPPER(FN) \
    > FN(unspec), \
    > @@ -5280,6 +5303,9 @@ union bpf_attr {
    > FN(xdp_load_bytes), \
    > FN(xdp_store_bytes), \
    > FN(copy_from_user_task), \
    > + FN(mkdir), \
    > + FN(rmdir), \
    > + FN(unlink), \
    > /* */
    >
    > /* integer value in 'imm' field of BPF_CALL instruction selects which helper
    [...]

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